It is well known that fuel level gauges are used to determine the filling height in a fuel tank and from that, in turn, the filling volume of the tank. Such devices are known in a variety of configurations. Fuel level gauges, for instance, for vehicles, are relatively simple in design and have fuel level sensors, for example, in the form of simple float constructions or the like. Over the years, industry has been unable to rely on an economical, maintenance-free and accurate system to measure the level of liquids in tanks. Level measurement systems are used to operate alarm gauges which indicate maximum and minimum liquid levels and control pumps, lights and signals.
Conventional fuel level sensing devices include a pickup tube and a return tube positioned adjacent a float. These devices are fully exposed to the contents of the tank and, in the case of vehicles, are subject to wild fluctuations in the liquid level of the tank due to shaking of the tank as the vehicle drives over rough terrain. These sensing devices are also subject to interference by any debris that might be floating within the tank. Moreover, the exposed pickup and return tubes, as well as the fuel level sensing device may become damaged by contact with the tank opening when the sensing device is installed within the tank.
Numerous design constraints are imposed upon fuel level sensors, wherein the fuel level sensors must be capable of withstanding corrosive environments, as the sensor is at least partially submerged in fuel and various types of fuel additives throughout its operational life. Also, the sensor is frequently subjected to extreme vibration and shock. In addition to these requirements, it is desirable that the sensor be of relatively low cost, compact in size, and fairly easy to manufacture and package.
Fuel level sensors as described in the prior art uses reed switch and are affected by temperature, pressure or depth. In existing fuel level indicator systems utilizing reed switches, a single reed switch is used within a hollow vertical tube and single or multiple ring magnets are used as magnetic elements. Because of the relatively short length over which a ring magnetic can influence the electrical condition of a reed switch, the existing fuel level indicator systems are useful only for measuring liquid level in relatively shallow tanks and for the purpose of indicating when a liquid level passes a predetermined point, such as an empty or dangerously low liquid level in a liquid storage tank.
Furthermore, existing systems having a reed switch utilize magnetic rings or other magnetic elements that set up a uniform magnetic field, the reed switch undergoes numerous changes in electrical condition as the tank in which it is utilized is emptied or filled. This repeated change of condition of the reed switch necessitates an elaborate electrical circuit to make the switch condition meaningful.
Thus, it would be advantageous to provide a fuel level sensor in order to provide an accurate, compact, and rugged fuel level sensor.